


Unnatural

by Anonymous



Category: Dr. STONE (Anime), Dr. STONE (Manga)
Genre: Alphas are the lesser, Brother/Sister Incest, Confession, Discord: The Kingdom of Shipping (Dr. STONE), F/M, First Time, Forbidden Love, Guilt, Incest, Knotting, Sibling Incest, Smut, TKS, TKSABOMONTH - Non Traditional ABO, TKSevents, TheKingdomofShipping, Vaginal Sex, first heat
Language: English
Status: Completed
Published: 2020-10-08
Updated: 2020-10-08
Packaged: 2021-03-07 16:48:09
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 2,595
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26900887
Author URL: https://archiveofourown.org/
Summary: Mirai had always loved her brother. She could go to him for anything. And when it comes the time to, she does. Tsukasa loves his sister from the bottom of his heart. He would never say no.
Relationships: Shishiou Mirai/Shishiou Tsukasa
Comments: 2
Kudos: 16
Collections: Anonymous, TKS Ryusui Ships and ABO Month - October 2020





	Unnatural

The smell was immaculate. And woah was the child who smelled it first. 

Tsukasa had just turned eighteen when his sister fell into heat. He was washing the dishes with great annoyance at his parents who once again left him to take care of things. Of course. He was the good little house alpha who takes care of the home. House alpha his ass! Just because he’s prone to his emotions doesn’t mean he’s some- some _stereotype_. 

His omega born sister on the other hand was always left to relax. Do what she wished and get what she wanted. But she was Tsukasa’s shining star in the dark bitter world that lay ahead for him. As much as people may think him jealous, he’s happy the girl was born an omega. Perhaps she would have a good life because of it. Not bound to the regress that was his own life- solely due to his biological nature. 

He thinks over this for awhile as his hands scrub furiously at the plate in hand. He’s a strong, unmarked alpha. His parents decided to keep him until the age of twenty and these are the years one would typically start to rebel. But he knew it would only cause his illness prone sister more stress than she needed. After all, soon her big brother would be taken away. And it’s thoughts like these that have Tsukasa remembering that he should stay calm and keep things discreet until the very end. 

He was nothing but a gene giver. One to serve under the country. While his sister is the one who will be able to give birth to many. To raise and protect and nurture. 

And just as her nature was. Of course one day she would hit the age where her nature presents itself. 

Tsukasa smells her right away. His eyes widen at the senses flooding him. Something tender and warm and delicious. Mouthwatering. He grits his teeth. That was Mirai. His eyes fixated on the sponge and plate over the sink. The suds drip down his fingers as he squeezes the sponge. Small, feeble footsteps make their presence in the kitchen. He can’t turn around. No, not when she is just behind him, shaking. Small fists ball into his shirt. His own breath hitches when he hears her take a deep breath. Her nose is pressed against him. 

“Big brother, it’s so hot.” With a voice so feeble it shatters his heart. The smell is intense now, calling to him like hung meat to a rabid coyote. 

“Mirai, you need to go to your room and lock the door, I’ll call mom.” Drool is gathering at the corners of his lips, he licks it away. He needs to stay focused.

“I can’t you smell too good.” She is smelling him again. He whimpers.

“Are you okay big brother?” There is a pause before she continues, “is this what heat is brother? Wanting to be this close with you?”

That’s right, she should have learned some in class already. She nuzzles her face into his back and he doesn’t know if the sponge in his hand will make it. Mirai moves to his side. From the corner of his eye he can see the top of her head, then her eyes as she looks up at him. 

“Brother,” she whimpers and leans against the counter, her legs spread as she lifts her dress to reveal herself and her small cotton panties. The baby blue fabric is darkened noticeably, dampened by her. 

He swallows so hard, eyes dilating. Tears manage at the corner of his eyes. Is this what they meant by alphas having no control? Surely they couldn’t mean he would be so feral as to defile his own flesh and blood. His shining hope in the darkness. His little Mirai. The reason he lived so patiently. But there is the slow crawl up his skin. The one that abandons logic and opens a path to something it confuses for love. 

There is a strum, a plain tune in his head that lets itself be known. The beginning to a symphony of admittance. 

He drops to his knees, and even then they are still head height. She is crying, so unsure and so scared. Tsukasa admits his own ruts had never been fun. Locked in the basement for days, hurdled over in pain and arousal, finally getting the decency of having a toy years after presenting. They wouldn’t do that to dear Mirai he is sure. She is a princess in her own right. 

His thumbs wipe at her tears, “it’s okay Mirai, I won’t let you suffer this.” He brings her close. She is on his scent gland immediately. That’s all it took for the delicate tune in his head to get louder Drowning out most of his reasoning. The alpha scoops her up, holding her head with a still damp hand. Slowly he moves to the basement, locking the door from the inside. 

“I’m scared.” She whispers to him as they descend. He nods at her. She wasn’t allowed in the basement. It smelled too much like him, too much like some desperately horny animal thing. And when he was down there he is sure his pained noises made her frightened. But when she is laid back on the bed- no, the nest that he had spent all his ruts in, she relaxes. 

She looks into his eyes again and he hesitates. Should he really be doing this? Was this normal? Surely, he will be beaten with an inch of his life if not killed. It’s too late. She too is succumbing to instinct, legs spreading for him. He stares intensely at the sodden cloth and the still seeping slick that is covering her poor white thighs. The smell is just as beautiful as the visual. Such a nice sweet honey smell, mixed with what he can only describe as sprinkles and cupcakes.

“Are you going to make love to me?” Her eyes are shining up at him. “Omegas are supposed to pick mates who they love right? Ever since I learnt that I..”

“Mirai... I’m your flesh and blood, would you feel such a thing towards mama or papa? Of course it wouldn’t be right.” He smiles gently at her. Really, what was he doing? Shes holding his old balled up clothes close to her and in her fists.

“You’re different from them.. if it isn’t right then what are you doing?” She asks, pulling her knees upwards only to show herself more to him, presenting without even knowing it. “You feel it too don’t you big brother?” 

There’s a broken note that plays, and his swallow only seems to get thicker. Mirai has always been the observant type. So smart and so sweet. He can hardly register when she is taking off that one piece of cloth that was separating him from everything. She giggles at his surprised expression. She is definitely growing alright. Her pink pussy is aroused, slightly puffed by blood and absolutely covered in slick. The hair that is still growing glistens with the wetness once pressed against it by her panties. 

“Please, it’s so hot Tsu, please make it better.” 

He bites his tongue. Slowly his hands feel up her legs. She gasps and twitches, eyes trained on him. He grabs her waist and pulls her closer- making her squeak in the process. He feels her inner thighs, listening to her whimpers. A thumb ghosts experimentally over her vulva. She whimpers in response. Slowly he tests his boundaries. Pulling at one of the fuzzy lips and watching her gasp. His thumb is soon coated with the slick as he teases up and down her slit.

“Big brother.” She has her eyes closed right now. Face red as a beet. 

The broadness of his palm alone was bigger than her. And he turns his hand to tease her there again. Getting her used to the feeling of being touched this way. The hum of his mind only grows, praising him for taking such good care of his sister. 

When he enters a finger she gasps. She’s clenching around him. Her hips wiggle in confusion at the new sensation. He thrusts the finger in and out of her dripping wet vagina, pressing up into the ridge and making sure his finger goes deep. 

“More,” she pleas, “my b-body wants more of you big brother.”

Her hands are knuckle white into the sheets of the nest. The best that once only smelled like her brother but now also reek of her own smell. 

He obliged to her desires. Pressing in a second finger. She only gets tighter. Her moans of strange pleasure are like the angels song to his ears. 

And soon he’s pressing in his third finger. Curving them upwards to stimulate more of the sweet sounds coming from her trembling body. 

“I’m a monster,” he says to her, thrusting the fingers at an easy pace for her to relax and become use to it all. “I shouldn’t be doing this to you, you need a proper mate.” Theres drool dripping down his chin. His own cock was begging to be buried deep within her. He doesn’t know if he has enough strength to resist it. But hopefully he would be able to. 

“Brother,” She is moving her hips with him too, “mate me, I don’t care, I love you.” What was she saying? Did she even realize the repulsion of her words? No, of course she doesn’t. The angel princess sister of his would never tell a lie. Her words are as honest as the warm sun in her eyes. The sun that over burned and blazed into their hearts. 

“I love you too Mirai.” His voice is quivering. He shouldn’t be using his other hand to unbuckle his pants and pull them down. He shouldn’t be pressing his hard cock against her thigh, pressing and rubbing it into her skin. 

When he looks up she looks mesmerized by it all. His dick, his face, his three fingers pushing deep into her. Their eyes meet and she’s so beautiful. So beautifully hypnotic. 

“You can put it in, please brother, I need it.” 

“Hold your breath.” Her face bunches up and she nods while grasping onto pillows. 

She seems sad and unsure about the loss of his fingers inside her. They’re drenched in slick and all he does with it is cover his erection, lubing it for her. And oh how he wished he didn’t enjoy the mere thought that it was _her_ slick that in fact was covering his cock. Stroking himself alone sends the melody to a high note chorus of need. 

Using a hand to lift one of her legs, he uses the other to line himself up with her entrance. Slowly pushing in. She gasps and her body shakes, trying to stay still as possible. Tears slip down her face but she hasn’t voiced her protest in this. Only the head is inside and Tsukasa is already seeing heaven. She’s so tight and warm around him, producing more of the slick just to get him in more. He can’t help but become lost. His now free hand finds her waist. He guides her back. She’s trembling and as his eyes focus on where he’s finally entered her he sees the blood of a virgin. 

She gasps and takes a deep breath. “It hurts Tsu, you’re so big.” She cries. 

“Do you want me to stop?” He asks without knowing if he even can. 

“No!” She cries, “please keep going, mate me!” 

Her continuous declarations have his heart throbbing and his cock twitching. Slowly he pushes deeper into her. Deeper and deeper until he reaches the hilt. How could such a small body hold such a thing? He looks up to her again. His eyes widen. 

Her smile reaches her eyes and meets her tears. Deep breaths coming from those trembling lips. Like she sits in an ethereal dream. 

“Tsukasa,” she uses his whole name and he swallows, “You’re my alpha now.” 

He nods to her. Mindlessly agreeing as she purrs our to him. 

The thrusts start slow. And she whimpers and moans to each one of them. Tsuaksa has all but lost himself the moment he fully entered her. The sounds of wet, skin slapping against skin vibrates throughout the room. Deep gutural moans make their way out of him. She’s nothing like the flesh light or the fantasies. Nothing like his hand or the fake hormones to satiate his rut. She was perfect. The perfect omega for under him. And he cannot help but to speed his actions. The gentleness becoming lost in the passion. 

“Mirai,” he growls, hovering over her. 

“Big brother,” She cries arms leaving the bed and wrapping around his neck.

He moves her body for her, hands pulling her to and from his thrusts. The smell filling his nose with them. Sex, love, mating, something surreal and painting a beautiful picture of heaven in his blank canvas mind. 

And then she asks for it. His knot. Saying the word like it were a curse word. She knew what knot was. Of course she did. Tsukasa has such a wonderfully smart omega sister. He lets tears run down his face as he does as she desires. Finally pushing one last time into her and letting her cunt stretch as the knot filled her. His deep driving cock pouring itself into her. She clenches around him and cries, her own orgasm consuming her. 

He holds her close, sweat dripping down his body and face. She deserves to have everything. Everything and more. And he would give her whatever she desires. That’s what runs through his mind as he holds her. She whimpers and nuzzles into him. 

“We’re mates now.” She says it so happily. 

Tsukasa, brain finding its ground again, holds her tighter. He knew if anyone found out he would be dead on the spot. Knew the repercussions of his terrible actions. 

They stay like that for awhile. Her breathing evens out. She is still very much in heat, but is at a nice low. Enjoying the company of her brother. 

“We have to go now, don’t we?” She asks him. “They’ll hurt you if we don’t go.”

Tsukasa slow blinks. Mirai was young, and she wasn’t really supposed to know much about society yet. But he assumes it’s only a natural guess from her. Younger folk are much more observant than people think. 

“Let’s go brother,” she holds him as if he is the fragile one here, “let’s go.”

He laughs to himself, because she’s pressing her lips to his. So honest. So sweet, just like an angel. 

“We’ll run away and be mates.”

“I don’t care about what mama and papa think, I’ve already decided my mate.” She whispers so low to him. 

“An omega’s word is law.”

She nods to him and begs for a kiss again, this time he obliged and presses his own lips against hers. 

“I love you big brother.” Her hands cup his face, “promise me we’ll run away.”

Tsuaksa looks into those deep melancholy eyes of hers. Blue as the mermaid sea they grew up by. When had his little princess grown up? Her words and actions sit deep with him. There is no turning back now anyways. And he rather fight to be with her and alive than leave her, knowing she wanted him. She chose him. 

“Yes,” he agrees, “we’ll run far away.”

**Author's Note:**

> Ahhhhhh okay okay 0///0 hope you liked! XD


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